A cover glass is usually disposed on the light incident side of a so-called crystal type photoelectric conversion device. However, when the photoelectric conversion device is installed on the roof of a house, reflected light from the cover glass may cause annoyance to neighboring houses. Therefore, in the cases where attention should be paid to reflected light, such as when the photoelectric conversion device is installed on the roof of a house, a cover glass is used which has asperities formed in its surface to disperse reflected light.
The shape of surface asperities has influence on the amount of light transmitted through a cover glass. Thus, there have been reported attempts to optimize the shape of surface asperities of a cover glass in order to improve the photoelectric conversion efficiency. For example, Patent Literature 1 discloses a cover glass having semi-spherical recesses formed in its surface. The shape and arrangement of the recesses of this cover glass are designed to increase the amount of light transmitted through the cover glass during daytime over the course of a year. When recesses are formed for such purposes, the depth of the recesses is set deeper than when recesses are formed only for the purpose of anti-glare.
In order to increase the light transmittance of a transparent substrate typified by a glass sheet, a reflection-reducing film is formed on a surface of the substrate in some cases. A most frequently used reflection-reducing film is a dielectric film obtained by vacuum deposition, sputtering, chemical vapor deposition (CVD), or the like. A fine particle-containing film containing fine particles such as fine silica particles is also used as the reflection-reducing film in some cases. The fine particle-containing film is formed by applying a coating liquid containing the fine particles onto the transparent substrate by means of dipping, flow coating, spraying, or the like.
With a reflection-reducing film formed on that surface of a cover glass which has surface asperities, the appearance may be significantly deteriorated due to uneven reflection. In order to reduce the deterioration in appearance, for example, Patent Literature 2 discloses a cover glass for photoelectric conversion devices that includes a reflection-reducing film and in which the shape of surface asperities of a glass sheet and the number of layers of fine silica particles stacked in valley portions of the surface asperities and on peak portions of the surface asperities are adjusted. This cover glass has a reflectance of 1.5% or more and 3% or less over the entire wavelength range of 380 nm to 780 nm for light incident on a side on which the reflection-reducing film is formed; thus, the deterioration in appearance due to uneven reflection is reduced.